Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Jan 25 2023 20:24:34 FOUS30 KWBC 252024 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 323 PM EST Wed Jan 25 2023 Day 1 Valid 2017Z Wed Jan 25 2023 - 12Z Thu Jan 26 2023 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE NORTHEAST... ....20Z special update... The Marginal Risk across the South has been removed with this update. Rainfall intensity over Georgia and Florida has been weakening over the past couple of hours and cloud tops have been warming on infrared satellite imagery as a line of convection has tracked east with an average speed of 15 kt. Further weakening of rainfall intensity is expected as the base of a shortwave trough extending from the Ohio Valley to the Lower Mississippi Valley lifts northward and the attendant cold front continues a steady progression toward the east. Otto ....16Z update... Portions of Florida/Georgia... 15Z regional radar imagery showed a forward propagating line of convection extending from southwestern Georgia, across the eastern Florida Panhandle and into the Gulf of Mexico. Recent MRMS hourly rainfall totals have been as high as 2 to 2.5+ inches between Tallahassee and Apalachicola Bay where short term training has occurred with line orientation matching the mean steering flow. Given the progressive nature of the preceding cold front and related moisture axis, the potential for localized flash flooding will come from small line segments that race out ahead and allow short term training which could support a quick 3-4 inches. Northern Mid-Atlantic to southern New England Coast... Rapid moisture transport with southerly 850 mb winds increasing as high as 70-80 kt (recent GFS/RAP forecasts) will increase precipitable water values into the 1 to 1.3 inch range this evening into the overnight hours into southern New England. Areas of heavy rain are expected to develop with brief training supporting the potential for hourly rainfall over 1 inch beneath divergent/diffluent flow aloft despite weak instability forecast by the recent model consensus. Low end potential for FFG exceedance on the 3 or 6 hour scales will be possible, with localized flooding possible as a result with snow melt across southern New England a contributing factor. Otto ....previous discussion follows... The upper level trough responsible for heavy rainfall in the Lower Mississippi Valley yesterday will phase with a northern stream trough and spread precipitation into the eastern third of the country today. Guidance appears to highlight two areas of particular concern. A complex of thunderstorms moving through the Florida panhandle will likely be enhanced by a strong cold front succeeding it. Instability will be shallow in northern Florida and Georgia, but a 50-60kt low level jet out of the south should supply ample moisture, on the order of 1-1.75in PWATs, into the region. That being said, soils will be relatively dry and Flash Flood Guidance fairly high so the threat of flash flooding should remain marginal. The heavy rainfall should subside over the Southeast by early this evening. Precipitation will begin as snowfall this morning in the Northeast before transitioning into rain this afternoon and evening. The aforementioned surface low will reintensify as it lifts through the Mid-Atlantic and Northeast. 60-70kt 850mb winds out of the south will overrun a warm front and supply anomalous moisture into the Northeast coast early Thursday morning. PWATs will be around 1-1.25in, representing 3-4 standard deviations above normal. Rain rates between 0.1-0.25 won't be too high, but moderately saturated soils and low FFGs could support instances of isolated flash flooding over vulnerable surfaces, including, but not limited to, urban areas. Kebede Day 2 Valid 12Z Thu Jan 26 2023 - 12Z Fri Jan 27 2023 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Otto Day 3 Valid 12Z Fri Jan 27 2023 - 12Z Sat Jan 28 2023 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Otto Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!_Dk_Ly6X_yGUkg_wQQcQ3JC2q3nVf2YPSQFXyzYpg6Gy= I1sW8xKtBVi-S6qI-VYkKXJdKvyPPaNh3iLM-k23IXm0K58$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!_Dk_Ly6X_yGUkg_wQQcQ3JC2q3nVf2YPSQFXyzYpg6Gy= I1sW8xKtBVi-S6qI-VYkKXJdKvyPPaNh3iLM-k237-JnwIo$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!_Dk_Ly6X_yGUkg_wQQcQ3JC2q3nVf2YPSQFXyzYpg6Gy= I1sW8xKtBVi-S6qI-VYkKXJdKvyPPaNh3iLM-k23VlJ_aNY$=20 $$ =3D =3D =3D To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM. --- SBBSecho 3.14-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .